Human bitterness detection thresholds of hop acids in beer and honey Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bk128d38p

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  • Alpha acids are found in the lupulin glands of hops cones. These acids have no bitterness of their own, but can be isomerized and subsequently hydrogenated to form bitter iso-α-acids and tetrahydroiso-α-acids respectively. Current literature values for the detection thresholds of iso-α-acid and tetrahydroiso-α-acid in lager beer have been reported using American Society of Testing and Materials (ASTM) method 679, a method commonly used to find detection thresholds of various compounds. ASTM method 679 is currently described as a “rapid method” and was a forerunner to ASTM method 1432, the current standard method for finding human detection thresholds. It has been argued that ASTM method 679 is statistically weaker than ASTM method 1432, as a group threshold found using ASTM method 679 is based on an individual “best estimate threshold” found using only one ascending series of 3-altrnative forced choice (3-AFC) presentations per panelist. The group threshold found using ASTM method 1432 is based on individual thresholds that are determined using data from 6 ascending series of 3-AFC presentations per panelist, the principle being that test repetition will help nullify moment-to-moment panelist variation. However, test repetition takes time, and the lack of repetition required for ASTM method 679 makes the method quicker and simpler to implement than ASTM method 1432. Current literature detection threshold values for both iso-α-acids and tetrahydroiso-α-acids in lager beer have not been found using ASTM method 1432. The primary objective of the research presented in this paper was to use the current ASTM standard method to determine updated threshold values for both iso-α-acids and tetrahydroiso-α-acids in lager beer. The secondary objective of this research was to compare threshold results from the same data set using ASTM method 679 and ASTM method 1432 to evaluate whether these methods provide statistically similar results. Findings showed that implementation of ASTM method 679 to find individual thresholds did produce results that were not statistically different from individual results found using ASTM method 1432. All group thresholds except the Day 1 tetrahydroiso-α-acid threshold found using ASTM 679 were also statistically in agreement with group thresholds obtained using ASTM method 1432. Beta acids, like alpha acids, are found in the lupulin glands of hops cones. Beta acids oxidize to form bitter compounds. Beta acids and tetrahydroiso-α-acids have been found to be miticidal against varroa mites, parasitic mites that feed off of and damage honeybees and bee larva. Though beta acids and tetrahydroiso-α-acids are FDA-declared GRAS substances, and will have no ill-effects on honey consumers, bees may transfer the bitter acids to their honey. Detectable levels of these bitter substances could lead to consumer rejection of honey from hives treated with beta acids or tetrahydroiso-α-acids. In a second experiment discussed in this thesis, the detection thresholds of beta acids and tetrahydroiso-α-acids were found in light clover honey. A method for the extraction and quantification of beta acids and tetrahydroiso-α-acids in beer and wort was modified and verified for the extraction and quantification of hops acids in honey. This method combined with group threshold data obtained in this experiment can be used in an industrial setting to determine whether the concentrations of beta acids and/or tetrahydro-iso-α-acids that may have been transferred to honey are above or below the human detection threshold.
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